1. Field of the Invention
The present invention relates to a virtual channel table for a broadcast protocol and a method of broadcasting using the same.
2. Discussion of the Related Art
Generally, a program and system information protocol (hereinafter, referred to as PSIP) of an Advanced Television Systems Committee (hereinafter, referred to as ATSC) standard for digital television broadcasting contains a virtual channel table (VCT). “Program and System Information Protocol For Terrestrial Broadcast and Cable,” ATSC Document A/65, 23 Dec. 1997, is hereby incorporated by reference for all purposes as if fully set forth herein.
The PSIP typically also contains an electronic program guide (EPG) and system information (SI). The PSIP is defined as the protocol of the ATSC standard for terrestrial and cable digital television broadcasting which parses encoded messages by using a moving picture experts group-2 (MPEG-2; ISO/IEC 13818-1) system to thereby provide various kinds of information on the broadcast programs (See ATSC document A165, 23 DEC 1997).
In other words, the PSIP transmits and receives audio/video data with MPEG-2 video and AC-3 audio formats, and contains several tables for transmitting information on the channel of each broadcasting station, and information on the programs on each channel. The PSIP has a primary function of conducting the audio and video services of the broadcast corresponding to a desired channel, and an additional function of conducting the electronic program service for the broadcast programs.
The channel information for the channel selection and the packet identification (PID) information for reception of the audio and video data are contained in the virtual channel table (VCT), and the electronic program service information on the broadcast programs on each channel is contained in an event information table (EIT). Also, the PSIP contains a system time table (STT) for time information, a rating region table (RRT) for transmitting information on the region and organization for program rating, an extended text table (ETT) for providing an additional explanation on the channel and broadcast program, and a master guide table (MGT) for management of the version of each table mentioned above and the packet identification (PID). These tables are transmitted in data units, which are called sections. Namely, all of the tables have one or more sections as a basic unit.
By way of example, the virtual channel table may be divided into 256 sections. A single section may contain information on several virtual channels, but information for a single virtual channel may not be spread over on two or more sections.
FIG. 1 is a diagram illustrating the bit stream syntax of a general virtual channel table for terrestrial broadcast, which has been described in the above-mentioned ATSC document A/65. The general virtual channel table contains a transport stream identifier, a major channel number, a minor channel number, a short channel name, a carrier frequency, a program number and the like, and contains additional information in the descriptor(s) thereof.
Referring to FIG. 1, the virtual channel table has the table identifier field of “0xC8,” and the value of the packet identification (PID) for the virtual channel table is “0x1FFB.” The version number field “version_number” represents the version value of the virtual channel table, the section number field “section_number” represents a corresponding section number, the last section number field “last_section_number” represents a last section number of the virtual channel table, and the section number channel field “num_channels_in_section” represents the number of whole virtual channels existing within the sections of the virtual channel table.
The short name field “short_name” within the statement in the “for_loop” represents the name of the virtual channel, and the major channel number field “major_channel_number” represents a major channel number among the virtual channels defined in the statement mentioned above. Each virtual channel number is connected to the major and minor channel numbers, respectively, and the major and minor channel numbers function as the user reference number for the corresponding virtual channel. In other words, the virtual channel table carries the data for each virtual channel through the statement of the “for_loop.”
The program number field “program_number” contains the information for connecting the virtual channel where the MPEG-2 program association table (PAT) and program map table (PMT) are defined, which corresponds to the program numbers in the program association table and the program map table. In this case, the program association table defines the components of the program every program number, namely, indicates the packet identification of the transport packet transmitting the program map table. The program map table defines the list and the annex information thereof on the packet identification of the transport packet transmitting the program identification number and the bit stream of the video and audio signals constituting the program.
The source identifier field “source_id” represents the program source connected to the corresponding virtual channel. In this case, the source means a specific source such as image, text, data or sound. The source identifier field “source_id” has a unique value in the transport stream transmitting the virtual channel table. The descriptor length field “descriptors_length” indicates the whole length of the descriptors of the corresponding virtual channel, and the additional descriptor length field “additional_descriptors_length” indicates the whole length of all of the additional descriptors of the virtual channel table.
FIG. 5 shows an exemplary list of descriptors for PSIP tables according to the ATSC standard.
FIG. 2 is a diagram illustrating an example of executing scheduled broadcasting by using four virtual channels in a broadcasting station.
By way of example, it is assumed that the scheduled broadcast as shown in FIG. 2 is executed through the four virtual channels, 51-1, 51-2, 51-3 and 51-8 in an arbitrary broadcast station and a virtual channel table composed of a single section is transmitted.
If the current time is 20:15, the system time table transmits the current time information. In this case, the channels 51-1 and 51-3 which are broadcasting at the current time (20:15) are defined as the “active channels.”
On the other hand, the channel 51-2 is not broadcasting at the current time and is going to be broadcast the next day, and the channel 51-8 is going to be broadcast next at 06:00. In this case, the channels 51-2 and 51-8, which are not broadcasting at the current time (20:15) and are going to be broadcast in the future, are defined as the “inactive channels.”
As a result, each channel may be an active or inactive channel, based upon an arbitrary point in time.
Within the PSIP, the virtual channel table should contain the active channels as required by the standard, and may also contain the inactive channels as recommended by the standard, for conducting the electronic program guide service.
Therefore, at the current time (20:15) the virtual channel table may contain information on all of the channels 51-1, 51-2, 51-3 and 51-8, and thus a digital television broadcast receiver or a digital cable broadcast receiver receives the virtual channel table to thereby provide the channel selection information to TV viewers.
However, as shown in FIG. 1, according to the bit stream syntax of the virtual channel table according to the ATSC document A/65, the digital television broadcast receiver or the digital cable broadcast receiver cannot discriminate between the active channels (for example, the channels 51-1 and 51-3) and the inactive channels (for example, the channels 51-2 and 51-8), when parsing the virtual channel table.
As a consequence, the TV viewers see a black screen because of the information on the inactive channels transmitted from the broadcast station for providing the electronic program guide. The black screen means the black background color is displayed on the screen when an inactive channel not broadcasting at a current time is selected. On the other hand, the character message “service not provided” is displayed on the screen of the black background color by the on-screen display function of the digital television broadcast receiver or the digital cable broadcast receiver. By way of example, if the TV viewer selects the channel 51-2 with a channel up key while viewing the channel 51-1, the audio and video data are not displayed because the channel 51-2 is an inactive channel, such that the black background color is displayed on the screen.
The above-mentioned problem may give many inconvenience to the TV viewers at a point of time when digital television broadcast receivers or digital cable broadcast receivers become popular and a large number of virtual channels are broadcast.